Italian naturalization process for US citizens (Florence)

We have been working to establish my wife's dual US-Italian citizenship by jus sanguinis, however we have been unable to obtain a marriage certificate for her grandparents from New York, and fear it is simply lost over time.

Absent jus sanguinis our intention is to retire to Italy with an Extended Stay Visa.

My questions are: For two US citizens seeking naturalization my understanding is that we are required to live in Italy for ten years.

1.) Is that ten year figure correct for non-EU citizens?

2.) How is this documented? Do we file some type of "Letter of Intent" with Italian immigration at the beginning of our Italian residency that we intend to seek naturalization or latter present ten years worth of Permesso di Soggiorno certificates and rental agreements with our naturalization application?

3.) How continuous must the residency be? Could we inadvertently lose our acquired time toward naturalization? Does leaving Italy for (lets arbitrarily say Protected content (or some other length of time) to visit the US or another country "resets the clock" back to zero? Is there a required minimum length of time required to be living in Italy each year?

Thank you for any help or advice you may offer, especially from anyone who has completed the naturalization process themselves.